Novel corona-resistant polyimide film and preparation method thereof

Abstract

The invention discloses a novel corona-resistant polyimide film and a preparation method, and relates to the technical field of polyimide films, and the film is prepared by carrying out film casting and high-temperature imidization on composite resin comprising the following components: polyamide acid resin obtained by polymerizing aromatic diamine and aromatic dianhydride, the molar ratio of the aromatic diamine to the aromatic dianhydride monomer is 1: (0.995-1.002). According to the novel corona-resistant polyimide film and the preparation method thereof, the corona-resistant polyimide film with excellent corona resistance and better mechanical property can be obtained through formula design innovation and film preparation process optimization, addition of a small amount of benzoxazine and reduction of the use amount of the corona-resistant filler; the method is simple in process, has low requirements on dispersion equipment, tape casting equipment and imine equipment, and is suitable for continuous industrial production. In addition, the method also has the advantage of lower cost, and compared with the traditional process, the method has the advantages that high-energy-consumption steps are reduced, and the production efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of polyimide film technology, specifically to a novel corona-resistant polyimide film and its preparation method. Background Technology

[0002] Polyimide film refers to a class of high molecular polymers containing repeating imide rings (-CO-NR-CO-) in the main chain. Its unique molecular structure endows polyimide film with excellent mechanical properties, excellent high temperature / cold resistance and excellent insulation properties. It is widely used in various extreme environments and special fields, such as aerospace, wind power generation, rail transportation, military equipment, new energy vehicles, etc., and is known as "golden film" and "one of the most promising engineering plastics of the 21st century".

[0003] Although polyimide film has excellent high temperature resistance and insulation properties, it is an organic polymer that cannot withstand long-term corona damage, which limits its application in high-voltage motors and variable frequency motors, and thus limits the widespread application of polyimide film in wind power generation, rail transportation and other fields.

[0004] In 1994, DuPont (USA), ABB (Switzerland), and Siemens (Germany) collaborated to develop the first corona-resistant polyimide film (Kapton CR), whose corona resistance lifetime was hundreds or even thousands of times that of ordinary polyimide films. Analysis of the corona-resistant polyimide film revealed that doping with nano-inorganic particles significantly improves its corona resistance.

[0005] Domestic research on corona-resistant polyimide films mainly focuses on the preparation, modification, and dispersion processes of corona-resistant materials. Patent CN101323672 prepared a polyimide film with good corona resistance by filling polyamic acid with metal oxides (one or more of titanium dioxide, aluminum oxide, and silicon dioxide) with a particle size ≤50 nanometers. Patents CN102161828, CN102532605, and CN102993749 increased the amount of filler in the polyimide film through the selection and surface treatment of nanofillers, thereby improving the uniformity of performance and the duration of corona resistance. Patents CN103029395, CN102490426, and CN1152275 all used a multilayer structure (at least one layer containing corona-resistant filler) to prepare corona-resistant polyimide films, improving the film's corona resistance while basically maintaining its mechanical properties.

[0006] The above methods for obtaining corona-resistant polyimide films generally follow the principle of increasing the amount of nano-inorganic fillers to improve the corona resistance time of the polyimide film. However, excessive filling with inorganic fillers will reduce the mechanical properties of the polyimide film, especially the elongation at break, which will affect the downstream electromagnetic wire wrapping. Surface treatment of nano-inorganic fillers can increase the filling amount while maintaining the required mechanical properties. However, in actual continuous production, the uniformity of the filler surface treatment, batch-to-batch variability, and the complexity of the production process all limit the application of this method. The production of corona-resistant polyimide films using a multilayer structure requires precise resin delivery and mixing equipment and precise coating equipment, resulting in complex processes, poor stability in continuous production, and increased production difficulty.

[0007] To address these issues, this invention proposes a novel corona-resistant polyimide film and its preparation method. Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] To address the shortcomings of existing technologies, this invention provides a novel corona-resistant polyimide film and its preparation method, solving the problems mentioned in the background section.

[0010] (II) Technical Solution

[0011] To achieve the above objectives, the present invention provides the following technical solution: a novel corona-resistant polyimide film, wherein the film is prepared by casting and high-temperature imidization of a composite resin comprising the following components:

[0012] A polyimide resin obtained by polymerization of an aromatic diamine and an aromatic dianhydride, wherein the molar ratio of the aromatic diamine to the aromatic dianhydride monomer is 1:(0.995-1.002).

[0013] The nano-inorganic filler is uniformly dispersed in the polyimide resin, and its mass accounts for 8-18% of the total mass of the film;

[0014] And a benzoxazine resin uniformly dispersed in the polyimide resin, the mass of which accounts for 0.08%-1.8% of the total mass of the film.

[0015] Preferably, the nano-inorganic filler is selected from one or more of nano-silica, nano-alumina, and nano-titanium dioxide, and its particle size ranges from 20 to 250 nm.

[0016] Preferably, the benzoxazine resin is selected from one or more of bisphenol A type benzoxazine, MDA type benzoxazine, DCPD type benzoxazine, phenol type benzoxazine, DOPO type benzoxazine, and phenolphthalein type benzoxazine.

[0017] Preferably, the aromatic diamine is selected from one or more of diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene or diaminodiphenyl ether.

[0018] The aromatic dianhydride is selected from one or more of pyromellitic dianhydride, biphenyl dianhydride, diphenyl ether dianhydride, benzophenone dianhydride, or hexafluorodianhydride.

[0019] A novel method for preparing a corona-resistant polyimide film includes the following preparation steps:

[0020] Step 1, Slurry preparation: Disperse the nano-inorganic filler in a solvent, first stir and impregnate at low speed, and then treat it by high-speed shearing or grinding to form a uniformly dispersed nano slurry;

[0021] Step 2, Resin Synthesis: In a solvent, aromatic diamine, benzoxazine resin and the nano slurry are added sequentially. After stirring and dissolving, dianhydride monomers are added in batches to carry out the polymerization reaction, resulting in a polyamic acid composite resin liquid with a viscosity of 350,000-450,000 centipoise.

[0022] Step 3, Film Formation and Imidization: The polyamic acid composite resin liquid is vacuum defoamed and then cast into a film. The solvent is removed by programmed temperature rise to form a polyamic acid gel film. Subsequently, the gel film is subjected to high-temperature imidization at 330-380℃, and the film is biaxially stretched during the imidization process to obtain the corona-resistant polyimide film.

[0023] Preferably, in step one, the solvent is selected from any one of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone, and the solid content of the resin liquid is 10-25% by mass fraction;

[0024] In step one, the low-speed stirring rate is 50-120 rpm, and the processing time is 20-40 min; the high-speed stirring or grinding rate is 1500-3500 rpm, and the processing time is 30-60 min; and the temperature throughout the entire process of step one does not exceed 45℃.

[0025] Preferably, in step two, the dianhydride monomer is added in four portions, with the mass addition ratios being 50%, 25%, 20%, and 3% respectively, and the interval between each addition being 40-60 minutes; the remaining dianhydride is used to adjust the resin viscosity.

[0026] The reaction temperature in step two is 30-60℃, and the stirring speed is 40-70 rpm.

[0027] Preferably, in step three, the process of removing solvent by temperature program includes: raising the temperature from room temperature to 100°C at 20°C / min and holding it at that temperature for 2-10 min; raising the temperature to 180°C at 10°C / min and holding it at that temperature for 10-20 min; and finally raising the temperature to 220°C at 10°C / min and holding it at that temperature for 5-10 min.

[0028] Preferably, in step three, the heating rate of high-temperature imidization is 10-25℃ / min;

[0029] When biaxially stretching the film, the longitudinal stretching ratio is 1:1.05-1.3 and the transverse stretching ratio is 1:1.01-1.1.

[0030] (III) Beneficial Effects

[0031] This invention provides a novel corona-resistant polyimide film and its preparation method. Compared with existing technologies, it offers the following advantages: This novel corona-resistant polyimide film and its preparation method, through innovative formulation design and optimized film-forming process, by adding a small amount of benzoxazine and reducing the amount of corona-resistant filler, yields a corona-resistant polyimide film with excellent corona resistance and good mechanical properties. The method is simple, requires minimal equipment (dispersion, casting, and imide), and is suitable for continuous industrial production. Furthermore, this invention offers a lower cost advantage, reducing high-energy-consuming steps and improving production efficiency compared to traditional processes. Experimental data shows that the polyimide film with added benzoxazine exhibits outstanding performance in corona resistance and electrical strength tests while maintaining good mechanical strength. This improvement not only enhances the overall performance of the product but also broadens its application range under high-voltage and high-frequency environments, demonstrating significant industrial application value. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Nano-inorganic slurries were prepared in the following manner for use in the examples and comparative examples described later:

[0034] 7.5 kg of silica with a particle size of 50 nm and 7.5 kg of alumina with a particle size of 200 nm were added to 170 kg of N,N-dimethylacetamide (DMAc) solvent and dispersed by stirring and shearing: first, the mixture was stirred at low speed (80 rpm) for 20 min to ensure that the filler was completely wetted by the solvent, and then stirred at high speed (3000 rpm) for 40 min. The slurry temperature was controlled at 40℃ throughout the process, and finally a uniformly dispersed and stable nano-inorganic filler slurry was obtained.

[0035] Example 1

[0036] Step 1: Add 8.2 kg of diaminodiphenyl ether (ODA) to 52.159 kg of DMAc solvent and stir (60 rpm) to dissolve, forming an amine solution;

[0037] Step 2: Add 0.163 kg of benzoxazine (MDA type) to the amine solution from Step 1 and stir (60 rpm) to dissolve it;

[0038] Step 3: Add pyromellitic dianhydride (PMDA) to the mixture from Step 2 to synthesize polyamic acid resin: First, add 4.465 kg of PMDA and stir (50 rpm) for 60 min to allow it to react fully; then add 2.232 kg of PMDA and stir (50 rpm) for 40 min to allow it to react fully; finally, add 1.786 kg of PMDA and stir (50 rpm) for 40 min to allow it to react fully.

[0039] Step 4: Add 37.617 kg of nano-inorganic filler slurry to Step 3 and stir (50 rpm) for 60 min;

[0040] Step 5: Add 0.446 kg PMDA to the solution from Step 4 in small amounts several times, stirring at 40 rpm and maintaining the temperature at 40°C. The synthesis reaction endpoint is reached when the resin viscosity reaches 400,000 centipoise.

[0041] Step 6: Vacuum defoam the corona-resistant polyamic acid resin solution from Step 5 for 4 hours, and then allow it to defoam naturally for 4 hours.

[0042] Example 2

[0043] Step 1: Add 8.2 kg of diaminodiphenyl ether (ODA) to 60.04 kg of DMAc solvent and stir (60 rpm) to dissolve, forming an amine solution;

[0044] Step 2: Add 0.154 kg of benzoxazine (MDA type) to the amine solution from Step 1 and stir (60 rpm) to dissolve it;

[0045] Step 3: Add pyromellitic dianhydride (PMDA) to the mixture from Step 2 to synthesize polyamic acid resin: First, add 4.465 kg of PMDA and stir (50 rpm) for 60 min to allow it to react completely; then add 2.232 kg of PMDA and stir (50 rpm) for 40 min to allow it to react completely; finally, add 1.786 kg of PMDA and stir (50 rpm) for 40 min to allow it to react completely.

[0046] Step 4: Add 23.8 kg of nano-inorganic filler slurry to Step 3 and stir (50 rpm) for 60 min;

[0047] Step 5: Add 0.446 kg PMDA to the solution from Step 4 in small amounts several times, stirring at 40 rpm and maintaining the temperature at 40°C. The synthesis reaction endpoint is reached when the resin viscosity reaches 400,000 centipoise.

[0048] Step 6: Vacuum defoam the corona-resistant polyamic acid resin solution from Step 5 for 4 hours, and then allow it to defoam naturally for 4 hours.

[0049] Example 3

[0050] Step 1: Add 8.2 kg of diaminodiphenyl ether (ODA) to 60.48 kg of DMAc solvent and stir (60 rpm) to dissolve, forming an amine solution;

[0051] Step 2: Add 0.291 kg of benzoxazine (MDA type) to the amine solution from Step 1 and stir (60 rpm) to dissolve it;

[0052] Step 3: Add pyromellitic dianhydride (PMDA) to the mixture from Step 2 to synthesize polyamic acid resin: First, add 4.465 kg of PMDA and stir (50 rpm) for 60 min to allow it to react completely; then add 2.232 kg of PMDA and stir (50 rpm) for 40 min to allow it to react completely; finally, add 1.786 kg of PMDA and stir (50 rpm) for 40 min to allow it to react completely.

[0053] Step 4: Add 24.05 kg of nano-inorganic filler slurry to Step 3 and stir (50 rpm) for 60 min;

[0054] Step 5: Add 0.446 kg PMDA to the solution from Step 4 in small amounts several times, stirring at 40 rpm and controlling the temperature at 45°C. The synthesis reaction endpoint is reached when the resin viscosity reaches 450,000 centipoise.

[0055] Step 6: Vacuum defoam the corona-resistant polyamic acid resin solution from Step 5 for 4 hours, and then allow it to defoam naturally for 4 hours.

[0056] Comparative Example 1

[0057] Step 1: Add 8.2 kg of diaminodiphenyl ether (ODA) to 51.82 kg of DMAc solvent and stir (60 rpm) to dissolve, forming an amine solution;

[0058] Step 2: Add pyromellitic dianhydride (PMDA) to the mixture from Step 1 to synthesize polyamic acid resin: First, add 4.465 kg of PMDA and stir (50 rpm) for 60 min to allow it to react completely; then add 2.232 kg of PMDA and stir (50 rpm) for 40 min to allow it to react completely; finally, add 1.786 kg of PMDA and stir (50 rpm) for 40 min to allow it to react completely.

[0059] Step 3: Add 37 kg of nano-inorganic filler slurry to Step 2 and stir (50 rpm) for 60 min;

[0060] Step 4: Add 0.446 kg PMDA to the solution in Step 3 in small amounts several times, stirring at 40 rpm and controlling the temperature at 40°C. The synthesis reaction endpoint is reached when the resin viscosity reaches 400,000 centipoise.

[0061] Step 5: Vacuum defoam the corona-resistant polyamic acid resin solution from Step 4 for 4 hours, and then allow it to defoam naturally for 4 hours.

[0062] Comparative Example 2

[0063] Step 1: Add 8.2 kg of diaminodiphenyl ether (ODA) to 59.52 kg of DMAc solvent and stir (60 rpm) to dissolve, forming an amine solution;

[0064] Step 2: Add pyromellitic dianhydride (PMDA) to the mixture from Step 1 to synthesize polyamic acid resin: First, add 4.465 kg of PMDA and stir (50 rpm) for 60 min to allow it to react completely; then add 2.232 kg of PMDA and stir (50 rpm) for 40 min to allow it to react completely; finally, add 1.786 kg of PMDA and stir (50 rpm) for 40 min to allow it to react completely.

[0065] Step 3: Add 23.556 kg of nano-inorganic filler slurry to Step 2 and stir (50 rpm) for 60 min;

[0066] Step 4: Add 0.446 kg PMDA to the solution in Step 3 in small amounts several times, stirring at 40 rpm and controlling the temperature at 40°C. The synthesis reaction endpoint is reached when the resin viscosity reaches 400,000 centipoise.

[0067] Step 5: Vacuum defoam the corona-resistant polyamic acid resin solution from Step 4 for 4 hours, and then allow it to defoam naturally for 4 hours.

[0068] Preparation of corona-resistant polyimide films:

[0069] The polyamic acid resins prepared in Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2 were coated and imidized to prepare corona-resistant polyimide films:

[0070] S1. The defoamed corona-resistant polyamic acid resin is evenly coated onto the steel strip (coating thickness 350μm), heated to 200℃ (0-100℃, heating rate 20℃ / min; 100-200℃, heating rate 10℃ / min), and held for 3 minutes to form a polyamic acid film with a certain supporting strength on the steel strip.

[0071] S2. The polyamic acid film from S1 is transferred to an imidizing furnace with biaxial stretching function via a needle plate (or chain clamp) for high-temperature imidization. The imidization temperature is 360℃, and the heating rate is 15℃ / min. The film is cooled from the high-temperature section to room temperature at a cooling rate of 30℃ / min. To improve the mechanical properties of the film, it is biaxially stretched during imidization: the longitudinal (MD) stretching ratio is 1:1.1, and the transverse (TD) stretching ratio is 1:1.02. A corona-resistant polyimide film with a thickness of 38μm is prepared.

[0072] Performance testing:

[0073] Tensile strength test: The test was conducted in accordance with GB / T 13542.2-2009; the results are shown in Table 1.

[0074] Elongation at break test: The test was conducted in accordance with GB / T 13542.2-2009; the results are shown in Table 1.

[0075] Electrical strength test: The test was conducted in accordance with GB / T 13542.2-2009; the results are shown in Table 1.

[0076] Corona resistance test: The test was conducted in accordance with GB / T 21707-2018; the results are shown in Table 1.

[0077] Table 1

[0078] Tensile strength / MPa Elongation at break / % Electrical strength / KV / mm Corona resistance duration / min Example 1 142.1 40 289 166 Example 2 156.4 50 280 115 Example 3 149.8 48 304 124 Comparative Example 1 122.5 30 254 145 Comparative Example 2 135.6 43 264 98

[0079] Furthermore, any content not described in detail in this specification is existing technology known to those skilled in the art.

[0080] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0081] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A novel corona-resistant polyimide film, characterized in that, The film is prepared by casting and high-temperature imidization of a composite resin comprising the following components: A polyimide resin obtained by polymerization of an aromatic diamine and an aromatic dianhydride, wherein the molar ratio of the aromatic diamine to the aromatic dianhydride monomer is 1:(0.995-1.002). The nano-inorganic filler is uniformly dispersed in the polyimide resin, and its mass accounts for 8-18% of the total mass of the film; And a benzoxazine resin uniformly dispersed in the polyimide resin, the mass of which accounts for 0.08%-1.8% of the total mass of the film.

2. The novel corona-resistant polyimide film according to claim 1, characterized in that: The nano-inorganic filler is selected from one or more of nano-silica, nano-alumina, and nano-titanium dioxide, and its particle size ranges from 20 to 250 nm.

3. The novel corona-resistant polyimide film according to claim 1, characterized in that: The benzoxazine resin is selected from one or more of bisphenol A type benzoxazine, MDA type benzoxazine, DCPD type benzoxazine, phenol type benzoxazine, DOPO type benzoxazine, and phenolphthalein type benzoxazine.

4. The novel corona-resistant polyimide film according to claim 1, characterized in that: The aromatic diamine is selected from one or more of diaminodiphenyl ether, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis(4-aminophenoxy)benzene or diaminodiphenyl ether. The aromatic dianhydride is selected from one or more of pyromellitic dianhydride, biphenyl dianhydride, diphenyl ether dianhydride, benzophenone dianhydride, or hexafluorodianhydride.

5. A method for preparing a novel corona-resistant polyimide film according to claim 1, characterized in that, The preparation steps include the following: Step 1, Slurry preparation: Disperse the nano-inorganic filler in a solvent, first stir and impregnate at low speed, and then treat it by high-speed shearing or grinding to form a uniformly dispersed nano slurry; Step 2, Resin Synthesis: In a solvent, aromatic diamine, benzoxazine resin and the nano slurry are added sequentially. After stirring and dissolving, aromatic dianhydride is added in batches to carry out the polymerization reaction, and a polyamic acid composite resin liquid with a viscosity of 350,000-450,000 centipoise is obtained. Step 3, Film Formation and Imidization: The polyamic acid composite resin liquid is vacuum defoamed and then cast into a film. The solvent is removed by programmed temperature rise to form a polyamic acid gel film. The gel film is then subjected to high-temperature imidization at 330-380℃, and the film is biaxially stretched during the imidization process to obtain the corona-resistant polyimide film.

6. The method for preparing a novel corona-resistant polyimide film according to claim 5, characterized in that: In step one, the solvent is selected from any one of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone, and the solid content of the resin liquid is 10-25% by mass fraction. In step one, the low-speed stirring rate is 50-120 rpm, and the processing time is 20-40 min; the high-speed stirring or grinding rate is 1500-3500 rpm, and the processing time is 30-60 min; and the temperature throughout the entire process of step one does not exceed 45℃.

7. The method for preparing a novel corona-resistant polyimide film according to claim 5, characterized in that: In step two, the dianhydride monomer is added in four portions, with the mass addition ratios being 50%, 25%, 20%, and 3% respectively, and the interval between each addition being 40-60 minutes; the remaining dianhydride is used to adjust the resin viscosity. The reaction temperature in step two is 30-60℃, and the stirring speed is 40-70 rpm.

8. The method for preparing a novel corona-resistant polyimide film according to claim 5, characterized in that: In step three, the process of removing solvent by temperature program includes: raising the temperature from room temperature to 100°C at 20°C / min and holding it at that temperature for 2-10 min; raising the temperature to 180°C at 10°C / min and holding it at that temperature for 10-20 min; and finally raising the temperature to 220°C at 10°C / min and holding it at that temperature for 5-10 min.

9. The method for preparing a novel corona-resistant polyimide film according to claim 5, characterized in that: In step three, the heating rate for high-temperature imidization is 10-25℃ / min; When biaxially stretching the film, the longitudinal stretching ratio is 1:1.05-1.3 and the transverse stretching ratio is 1:1.01-1.1.